A technology disclosed in the present specification relates to an image processing method and an image projection device that processes an image for projecting a reproduced image of media or a computer screen, for example, on a screen, and particularly to an image processing method and an image projection device that corrects geometrical distortion of an image projected on a screen.
Recently, there have been more occasions in which images received by a television, images reproduced from media such as a Blu-ray Disc, and personal computer (PC) screens, for example, are projected on a large-sized screen using a projection-type image display device so that a plurality of persons view them or make presentations. In addition, there also exists a small-sized projection-type image display device (pico-projector) that is used on a palm or mounted on a mobile device system.
When an image is projected on a screen, there occurs a problem of geometrical distortion in which the image is projected in a shape different from a shape of an original image, such as distortion of an image projected diagonally relative to a projected body (a screen wall face, for example) in a trapezoidal shape. The automatic correction function of geometrical distortion of a projection image generally includes projection of a test pattern on a screen, photographing of an image of the test pattern projected on the screen with an incorporated camera, obtaining of three-dimensional information based on the obtained positions of four corners of the screen and positions of four corners of the test pattern, and correction of geometrical distortion of the projection image (see JP 2011-193332A, for example). When a projection image is distorted in a trapezoidal shape in a vertical direction, the projective transformation is performed so that a display image is intentionally distorted in an opposite direction to geometrical distortion of the projection image on a screen, whereby a presentation image projected on the screen has the shape same as the shape of the original image (a quadrangle, for example).
The distorted image before correction projected on the screen by the projection-type image display device corresponds to a projectable maximum range. Therefore, it may be necessary to form a presentation image projected on the screen after correction, inside the distorted image before correction.
For example, there is proposed a projector in which correction frame image signals corresponding to an outline of an image after the trapezoidal distortion of a projection image is corrected are generated and a correction frame image by the correction frame image signals is displayed on the projection image by input image signals, so as to compare the size of the projection image after correction of trapezoidal distortion with the size of the projection image before correction (see JP 2009-251542A, for example).